LAUSD Superintendent Ramon Cortines said that the district received a threat in the form of an email that mentioned backpacks and other objects. Cortines said the threat was broad and was made against multiple schools.
According to LAPD Chief Charlie Beck, the email was very specific to LAUSD campuses and it threatened violence and mentioned "assault rifles" and "machine pistols."
Hours later, U.S. Rep. Adam Schiff, D-Calif. with the House Intelligence Committee said preliminary investigation indicates the threat sent to LAUSD is believed to be a hoax.
Threat came from outside the United States
Two law enforcement officials familiar with the investigation told ABC News that the email threat came from outside the country and named "a fairly large number" of specific schools.
Beck says the email was routed through Germany but that police believe its origin was much closer.
Cortines called this threat "rare" and said the decision to close all schools for the day was made out of an abundance of caution. He said the Dec. 2 attack in San Bernardino that left 14 people dead influenced the decision.
"I, as the superintendent, am not going to take the chance with the life of a student," Cortines said at the news conference.
All LAUSD campuses to be searched
Cortines said all schools within the district will be searched by law enforcement by the end of the day. As of shortly before 1 p.m., LAPD said 75-80 percent of all schools were cleared and they hope to have the rest cleared by 4 p.m.
The district said all after-school activities have been canceled.
Beck said he agrees with Cortines' decision to close all schools following the threat. The chief said criticizing the decision to close LAUSD schools is "irresponsible."
"It is very easy in hindsight to criticize a decision based on results that the decider could have never known," Beck said at a news conference. "It is very easy to criticize a decision when you have no responsibility on the outcome of that decision."
Several LAUSD school bus drivers told Eyewitness News that they were called back by their dispatchers to their respective bus depots Tuesday morning.
All students who were already at their schools were sent back home. Parents were urged to make arrangements to pick up their children if they were already dropped off on campus and also bring proper identification.
"We need the cooperation of the whole of Los Angeles today," said school board President Steve Zimmer. "We need families and neighbors to work together with our schools and with our employees to make sure our schools are safe throughout today."
Los Angeles Mayor Eric Garcetti released a statement regarding the LAUSD closures, urging families to remain calm. He said the city's Emergency Operations Center has been activated and the MTA will provide free bus rides to all LAUSD students.
The FBI is aiding in the investigation led by LAUSD police.
Other school districts around Southland not affected
Because the threat was specific to the LAUSD, schools in Pasadena, Burbank, Glendale, Altadena, Torrance, Simi Valley, Culver City, Glendora, Santa Monica-Malibu, El Segundo, Hermosa Beach, Newport Beach, Costa Mesa and Palos Verdes Peninsula were not affected.
All schools in Hawthorne, except for Cimarron Elementary School, which is part of LAUSD, are also open as scheduled. Los Angeles Trade Technical College, Los Angeles City College and Pierce College said their campuses will be open Tuesday.
Similar threat made against New York City schools
A similar threat against New York City schools was made via email Tuesday morning and it was very similar in nature to the email threat against LAUSD. Police in New York deemed it not a credible threat and did not close schools.
The LAUSD is the nation's second largest school district. The district includes 640,000 students in kindergarten through 12th grade and more than 900 schools and 187 public charter schools.
The district spans 720 square miles including Los Angeles and all or part of more than 30 smaller cities and some unincorporated areas.
If you have any questions regarding the closure, you can contact the LAUSD at (213) 241-2064 or at www.lausd.net.
ABC News and the Associated Press contributed to this report.